The studies described in this proposal represent a systematic and integrated investigation of hormonal and nutritional factors involved in the control of hepatic protein metabolism in the rat, using the whole animal, the perfused liver and isolated hepatocytes as experimental models. The objectives are 1) to investigate the effects of diabetes, insulin, glucagon, fasting, protein depletion and amino acid deprivation on liver protein synthesis; 2) to distinguish effects of these conditions on the synthesis of secretory proteins, particularly albumin, from those on retained intracellular proteins; 3) to identify the biochemical site(s) of action of each hormonal and nutritional factor; 4) to establish a liver cell-free system in which effects on the partial reactions of peptide-chain initiation can be studied; 5) to investigate the utilization of cytoplasmic mRNA, particularly albumin mRNA, by following its distribution between membrane-bound polysomes, free polysomes and ribonucleoprotein particles and by determining its poly(A)-chain length, 5'-capping and turnover; and 6) to integrate effects obtained in vitro in an attempt to explain the alterations in liver protein synthesis which occur in the whole animal in response to changes in hormonal and nutritional status. Identification of control sites and regulatory mechanisms will involve the application of a number of biochemical and molecular biological techniques that are currently employed in our laboratories, such as identification and quantitation of intermediary initiation complexes, separation of membrane-bound and free polysomes, immunochemical quantitation of albumin and albumin-synthesizing polysomes, quantitation of mRNA by cell-free translation and cDNA hybridization assays, and size determination of the average poly(A) length of mRNA.